In recent years, the sales of small aircrafts with capacities from several to dozen passengers have greatly increased due to their high convenience and enhancement of fuel efficiency. Demands on them will increase in future as a transport means that helps airliners' air transport. They are expected to create a new market that activates the aircraft industry. However, the number of accidents involving small aircrafts with capacities of several passengers is much more than that of large airliners. It is a factor hindering the spread of small aircrafts.
Most of such accidents are caused by maneuvering errors due to an increase in workload on less experienced pilots. Therefore, it is the urgent need for development of the aircraft industry to reduce load on pilots not only in normal flight conditions but also in bad weather conditions and in the case of trouble where the workload is likely to increase.
In such circumstances, a motorized aircraft in which a propulsion unit such as a propeller is driven by electric motors, which is coming closer to reality in recent years, has high fuel efficiency. In addition, various maneuvering automation technologies using electric motors with extremely higher controllability and responsiveness in comparison with an internal-combustion engine has been proposed (see Non-Patent Literature 1).
Providing high maintainability, the various maneuvering automation technologies using electric motors are aimed at enabling many people to easily handle aircrafts like automobiles without needing special trainings. Such maneuvering automation technologies using electric motors can reduce the maneuvering errors, load, and the like of pilots as described above. Further, the maneuvering automation technologies using electric motors can lower the accident rate. Therefore, the maneuvering automation technologies using electric motors can promote the spread of small aircrafts.
It should be noted that, for applying such technologies, it is always necessary to prevent the maneuvering automation technologies as described above from being broken without requiting special maneuvering techniques and correction operations of pilots. That is, it is necessary to continue stable flight as in normal flight even during emergency.
Here, examples in which workload greatly increases in an unexpected situation can include great reduction and lost of thrust, which are caused by propulsion system trouble in flight. In such a case, a pilot is required to conduct many operations such as thrust recovery operations and search for an emergency landing point at the same time. It increases workload on the pilot and induces maneuvering errors.
It is conceivable that, for solving such a problem, the provision of a plurality of propulsion systems as described in, for example, Patent Literature 1 can prevent a complete loss of thrust.